It is well known in the prior art, electrical energy may be generated from the “free” energy produced by the mixing of two ionic solutions by a reversed-electro-dialysis or pressure retarded osmosis (PRO) processes. This process utilizes two ionic solutions of differing concentrations and temperature ranges, passing the solutions through a Reversed-Electro-Dialysis membrane stack, the dilute and concentrated solutions entering on either side of the membrane layer, causing solute to pass from the concentrated side to the dilute side, creating the generation of an electrical output across the electrodes located at either end of the membrane stack. The resulting electrical output is a function, generally speaking, of the difference in the concentrations of the inputted solutions, the type of salts utilized and the corresponding enthalpy of solution of a particular salt, and the characteristics of the membrane and electrodes utilized including the number of membrane cell units.
In the case of large supplies of available aqueous solutions, such as seawater and municipal fresh water supplies, reserved-electro-dialysis (“RED”) or pressure retarded osmosis factories constructed require a continual replenishment of ionic solutions used to conduct their salinity-gradient processes, causing the need to discharge of spent brine into the environment. The solution sources in most RED systems utilize natural fresh water sources (such as rivers) and natural saltwater sources (such as the ocean, or a salt water lake) these sources of solution contain impurities that damage and reduce the efficiency of the RED system's membrane stacks or in the case of pressure retarded osmosis, these impurities cause fouling of the membranes. This situation limits the overall efficiencies of such an open-ended, reversed-dialysis system.
Modifications have been developed to address the limitations of such an open system design, including, for example, Loeb, U.S. Pat. No. 4,171,409, Oct. 16, 1979. Loeb designed a contained or closed system, eliminating the need to continually replenish the ionic solution inputs, as well as eliminates the need to dispose of discharged outputs. Yet the wattage and power density of the ionic solution per unit volume generated by Loeb's system is low due to various factors including the temperature ranges preferred by Loeb. (T-high 100 degrees C./T-low 25 degrees C., resulting voltage 0.170 watts/m2 in a 0.57 NACL aqueous solution. FIG. 3)
Other factors effecting the efficiency of a reversed-dialysis system like Loeb's, include the type of ionic compounds selected; the state of the art and type of membranes and electrodes selected including the types of shuttle carriers used within the electrode units (the rinse solution); whether or not a single separator or thermal unmixing unit (processing tank) is utilized; the shapes, design and materials comprising such processing tanks and their corresponding entry pipettes; the use of various shapes, designs and materials of heat exchangers and manifold systems; the use of one or more buffering tanks; the use of a compressor refrigerant cycle (heat pump as a heat source) and the capture and absorption of ambient air heat supplies back into the contained system; and the use more than one RED unit, using a thermodynamically opposed solution all may be utilized to create further efficiencies.
What is needed is an efficient contained ionic salt-gradient system which is able to make a significant supply contribution to the existing electrical power markets, in particular, performing an air cooling function so as to limit the heat foot print heat energy of manufacturing, especially of energy manufacturers.